The present invention relates to microwave radio frequency waveguide feed systems, and more particularly to a high-isolation and polarization diverse circular waveguide orthomode feed for reception of Direct Broadcast Satellite (DBS) television and Internet satellite downlink services that operate worldwide.
The widespread demand for high-quality video, audio, and data communications via satellite has resulted in the need for additional bandwidth and better cross polarization rejection as well as reduced interference from noise or adjacent frequency operation. As a result, satellite broadcast systems are operating over broader and higher frequency ranges and implementing sophisticated methods to reduce interference and improve the intelligibility of communication signals that limit their operating capability. However, the radio frequency apparatus that operate at higher frequencies and with broader bandwidth require considerable design attention and often result in multiple and complicated waveguide feeds in order to account for electric and magnetic field behavior that exists inside the microwave waveguides that propagate their signals.
Also, in order to maintain reliable communication, transmit and receive systems must possess polarization compatibility and be of rugged design. Polarization compatibility is that property of a radiated wave of an antenna that describes the shape and orientation of the electric field vector as a function of time. It further complicates the waveguide feed design because electromagnetic energy may be transmitted in arbitrary linear, right-hand circular, left-hand circular, or elliptical polarization. Reliable system performance must be maintained while satisfying mechanical requirements for structural mounting and small size. This includes careful selection of electrical system components such as tuning studs or screws that are used on-board aircraft or satellite platforms that are particularly susceptible to the vibration and shock environment that jeopardize performance and erode component reliability.
It is well known in the art that square waveguides produce mode patterns that allow high efficiency injection or removal of energy for linear polarized electromagnetic waves using probe coupling, which results in orthogonal linear polarizations of high-isolation needed to reduce noise and unwanted adjacent frequency interference. A popular method of transforming linearly polarized signals into a circular polarized signal and vice versa in square waveguides is accomplished by using septum polarizers. The septum conversion process provides a 90xc2x0 differential phase shift between two propagating orthogonal linearly polarized electromagnetic waves. Satellite systems, however, typically operate with circular polarization, which propagates well in circular waveguides, but generates undesirable cross polarization components and poor isolation when using orthogonal probe coupling methods in planar orientation. Thus, reduced propagation efficiency and increased attenuation of radiated signal intelligence occurs.
In order for optimum antenna efficiency, gain, and signal-to-noise ratio, the cross polarization components that result in a circular waveguide from the two orthogonal polarizations that comprise the elliptically polarized wave must be minimized. Methods in the art to condition the circular polarized wave and minimize cross polarization components employ elaborate conversion schemes that transform the elliptically polarized electromagnetic waves by using polarity converters, filters, circular-to-rectangular waveguide transitions, and multiply configured septum polarizers and tuning studs, each of which are difficult to design, operate with poor stability in harsh environments, and possess high cost and large size.
The present invention is a microwave feed assembly of simple, elegant, rugged, and scalable design that incorporates the desirable characteristics of broadband operation, polarization diversity, high-isolation between the orthogonal linear polarizations using septum polarizer methods, low insertion losses, small size, and applicability to a broad family of antennas.
The present invention relates to a high-isolation and polarization diverse circular waveguide orthomode feed for microwave frequency antennas. In one aspect of the invention, the waveguide feed supports transmission or reception of any arbitrary linear, right-hand circular, left-hand circular, or elliptical polarized microwave signal while achieving desirable performance over a wide range of frequencies with small size. In another aspect of the invention, the waveguide feed incorporates high cross-polarization rejection of unwanted linear cross polarization components when operating in arbitrary linear mode. In yet another aspect of the invention, the waveguide feed employs high probe-to-probe isolation for rejection of undesired cross-polarization when operating in circular or elliptical polarization mode. A waveguide feed assembly is disclosed, which comprises a combination of a circular waveguide segment, septum polarizer, and a novel arrangement of planar electric field probes positioned in the septum bifurcated region to achieve high-isolation, broad bandwidth, and polarization diversity.
It is an object of the present invention to provide a microwave waveguide feed system that can transmit or receive arbitrary linear, right-hand circular, left-hand circular, or elliptically polarized electromagnetic waves.
It is another object of the present invention to provide a microwave waveguide feed system that will support operation over a broad range of frequencies.
It is yet another object of the present invention to provide a microwave waveguide feed system with probe-to-probe isolation when rejecting undesired linear cross polarization of the two orthogonal linear polarizations that comprise circular or elliptical polarized electromagnetic waves.
It is yet another object of the present invention to operate in a non-radiating application such as a conversion from circular waveguide to a coaxial waveguide.
It is a feature of the present invention to provide a waveguide assembly that is polarization diverse for operation with arbitrary linear, right-hand circular, left-hand circular, or elliptically polarized electromagnetic waves.
It is another feature of the present invention to provide a compact, reliable, and simple to manufacture waveguide assembly that uses common materials and is suitable for reflector type antennas used to meet minimal radome swept volume applications by reducing the axial length of the waveguide assembly.
It is an advantage of the present invention to provide a waveguide assembly that is low cost, rugged, and applicable to a broad family of microwave antennas.
It is another advantage of the present invention to provide a microwave waveguide feed that can operate as a stand-alone microwave antenna system.
It is yet another advantage of the present invention to provide a waveguide assembly that incorporates design characteristics that are scalable to any frequency of microwave operation.
These and other objects, features, and advantages are disclosed in the specification, figures, and claims of the present invention.